I use bbpress since version 2, it perfectly integrate itself into buddypress/wordpress that's true.

But there's some crucial points for a production tool that are terrific with this plugin :

- updates are a mess, i just update to 2.2 version, the auto update don't worked, ok i paste new files.
And OMG every previous repertory are changed in the plugin, ok so i have to rewrite a lot of stuff and plugins dependencies myself. It tooked hours.

-performance for very large boards are really poors.
Because bbpress uses wordpress hooks, and not dedicated hooks (like user_roles for a board is a killing db engine) if you plan to build a very large board without a dedicated over powered server you'll need to hack the plugin yourself.

-moderation tools are really very very poors, as an example : "ban user" function and button for moderators don't exist.
Have you ever seen a forum without ban tools for spammers and undesired users? Don't search an answer, because it doesn't exist, every boards have this basic function.

- the doc of bbpress is so poor and messy, that your best option to learn and understand about this plugin is to open its files.

- and finally the crucial thing, surely the most important one : export/import forums are totally buggy.

If you plan to change your server, you'll have to mirror your old one, because if you don't your going to have hours of headache working on dbs and bbpress. If you plan to "backup" the board... Well good luck, you'll have to set up yourself admin tools in linux to backupd dbs and files.

So yes it's free, it's the best solution for a complete forums integration in wp/buddypress, but if you plan to use it for a big website, you'll have to struggle with this plugin for a long long developper nightmare. And you're not sure to beat the monster at the end ;)